This invention relates to improvement on cement, products thereof, and molding material to yield higher physical strength, better thermal resistance and water resistance, and a method for producing them.
This invention also relates to an improvement on a concrete member to yield higher physical strength, better thermal resistance and water resistance, and a method of producing the same.
There are known various organic or inorganic compounds available for molding materials, adhesives, laminates and other materials used for various fields such as civil engineering and construction industries, transportation industries of cars or railroads, chemical industries, other general mechanical industries and so on.
Hydraulic cement has been generally used as mortar or concrete mainly in civil engineering and construction industries. The cement is combined with more than 25 weight % of water and aggregate is added thereto to produce cement products. The cement products have low flexural strength of 50 to 100 kgf/cm.sup.2 (5 to 10 N/mm.sup.2) although they have high compressive strength and they conventionally have reinforcing bars used therein. In order to improve the flexural strength of the cement products, there are added short glass fibers or carbon fibers thereto. However, their flexural strength rarely exceeds 400 kgf/cm.sup.2 (40 N/mm.sup.2).
In general, the cement products have higher physical strength as the amount of water used is lowered, and also as the amount of blow-holes included therein is lowered.
For example, Japanese Application Publication No. 43431/1984 discloses cement products having extremely high flexural strength without any fibers included therein and without being molded under high compressive pressure. These cement products can be produced by kneading hydraulic cement, water and water organic polymer with each other while high shearing force is applied thereto by a double roller mill so that sizes and rates of blow-holes in the cement products are limited.
The cement products disclosed in The Japanese Application Publication have higher flexural strength because it is cured by combining hydraulic cement with 7 to 30% of water relative to hydraulic cement. However, the cement products, although having flexural strength improved, disadvantageously have physical strength lowered when they are immersed in water. They also have water resistance lowered due to their swelling when they are immersed in water. The disadvantages are present because of the cement products including water organic polymer.
In order to improve water resistance of the cement products, Japanese Patent Application Laying-Open No. 206342/1988 discloses cement products including an isocyanate compound reacted with the hydrophilic group of the water organic polymer of the aforementioned cement products. Such isocyanate compound may be added to the components of the cement products before they are kneaded or while they are kneaded. Also, they may be impregnated with isocyanate compound after they are kneaded, but before they are cured or after they are cured.
However, such material has a disadvantage during kneading and molding because isocyanate compound is virulent and has a strong irritating smell. Furthermore, urethane derivative which is the main reactant produced by reacting the isocyanate compound with the hydrophilic group disadvantageously has lower thermal resistance.
Formaldehyde has been used also for molding materials, adhesives and laminates. Such molding material including formaldehyde is obtained by combining formaldehyde resin precursor with filler such as wood flour, pulp, diatomaceous earth or the like, curing agent, lubricant, coloring agent and/or other additives, grinding and classifying them. In order to lower fragility of such molding material and improve flexural strength thereof, there has been added thereto filler of fibers such as cotton fibers, flax fibers, glass fibers or the like.
Such molding material is molded by compression molding, transfer molding or injection molding to produce mold goods. Such mold goods have flexural strength of 500 to 1000 kgf/cm.sup.2 (50 to 100 N/mm.sup.2) unless there is used filler of fiber material such as glass fibers or flax fibers.
However, such molding material of formaldehyde cannot have high flexural strength of more than 100 N/mm.sup.2 without any filler of reinforcing fibers. If reinforcing fibers are added to formaldehyde, then the reinforcing fibers are cut when the molding material is produced and oriented when it is molded. The cutting and orienting of the fibers causes the mold goods to have the physical strength varied and an orientation provided thereto.
In addition, since the molding material has fluidity lowered due to the filled fibers, the molding material disadvantageously fails to pervade all parts of the mold, which prevents the molded products from having a smooth surface.
Conventional concrete members have been manufactured by placing freshly mixed concrete in a mold of steel, wood or FRP provided in factories or working spots. It will be noted that they may be advantageously manufactured by using permanent molds of precast concrete because such permanent molds are integral to the concrete members and not required to be removed. If the permanent mold is formed of concrete having high durability, then the entire concrete members will have durability improved. The concrete members may have reinforcing bars used therein.
However, conventional concrete placed in the mold of steel, wood or FRP has poor wear resistance and water tightness. Furthermore, the concrete members will have durability lowered due to rust of the reinforcing bars. This is caused by chloride permeating the concrete members through fine cracks or honeycombs therein, which are in turn produced due to poor operation of the concrete construction or poor curing of concrete material therefor.
Although the property of concrete itself may be improved by adding admixtures such as fibers or silica fumes to concrete material, such improvement on the entire concrete members is undesirably expensive.
Although the entire concrete members are able to have their durability improved if permanent molds of precast concrete having high durability are used, they still have no flexural strength improved.
Such permanent molds of precast concrete are relatively thicker and heavier, which causes assemblies thereof to be troublesome. Of late, the concrete members are required to be relatively thinner and lighter.